"I knew early on that she was the one for me," Manganiello, 33, told PEOPLE Saturday night at Seminole Casino Coconut Creek's "Haunting" weekend event in south Florida. "I wasn't expecting to get married just yet, but when I felt this was the right situation for me, I decided to go ahead."
In September, Manganiello, who plays the wondrous werewolf Alcide Herveaux on HBO's hit vampire series, told PEOPLE that Marie is a "great dresser, gorgeous, tall, sweet, and she makes crazy English breakfasts."
Although the couple met at 2009's Super Bowl in Tampa, the actor didn't start dating Marie for several months. But soon after he was cast on True Blood, they started seeing each other.
Now, he is enjoying every minute of their engagement.
"It was very romantic to propose in Italy, where my family comes from," the actor, 33, tells PEOPLE. "We are both excited and plan to enjoy the moment."
While they have yet to set a time or place for the nuptials, Manganiello says they are working on several scenarios, including a return to Italy.
"We absolutely loved Italy, but have several ideas of where we will marry and haven't made a decision yet," he tells PEOPLE. "We are working on plans, talking through some ideas and then we will decide. Right now, we are just happy being engaged and want to enjoy this time in our lives."